Tissue culture methodologies allow physiological reactions and occurrences to be studied outside the organism without the influence of other biological reactions.
Incubation of tissue slices for short periods (hours) was introduced for biomedical studies in 1923 by Warburg. Prolonged incubations (days/weeks) were, in practice, not possible until the 1950's, following the introduction of antibacterial and antifungal antibiotics.
There must be uniformity between individual tissue sample for uniformity and reproducibility among experiments for an effective tissue culture methodology. In the past, the production of homogeneous tissue slices from fresh tissue samples has been difficult and dependent on the skill and the experience of the technician. Attempts to produce tissue samples which are uniform in dimension have been met with problems including irreproducibility of slice thickness, contamination of tissue samples and irregular, nonreproducible trauma to the tissue adjacent to the cutting surface.
In U.S. Pat. No. 5,148,729, the applicant disclosed a biological tissue slicer which allowed an inexperienced technician to produce nearly identical tissue slices in an aseptic environment while minimizing tissue trauma. The invention included a blade held in a blade holder between two pins while one or more permanent magnets provide a constant downward pull on the blade and blade holder. The design eliminated need for readjustment or tightening which are opportunities for contamination. The reproducibility of tissue slices is increased as vertical "chatter" of the blade decreases. Also, the exposure of the tissue sample to the blade is limited to reduce the extent of trauma to the cut surface of the tissue.
Also it is difficult to obtain proper slices from very small samples, which may consist of an entire organ from an experimentally sacrificed animal, for example.
A common practice in sampling tissue involves cutting a cylindrical core from an organ or quantity of tissue with a coring tool or similar device. The cylindrical core, however, leaves a large amount of tissue in between the cores which is unusable for slicing.
An often overlooked factor for obtaining quality tissue slices is the proper orientation of the tissue sample within the slicing machine. Coring cylinders from some tissues, for example, liver, usually result in major blood vessels being oriented parallel to the plane of slicing. When thus oriented, the cutting blade of the tissue slicer comes in tangential contact with the tough connective tissue of the blood vessel wall and often fails to cut it, shredding instead the remainder of the slice. The vessels extend across the bottom of the core as the blade cuts pieces of tissue about the large longitudinal ridge of connective tissue formed across the lower surface of the core. This results in high quality cuts from the first 3 to 4 slices of a core but all subsequent cuts are shredded or contain holes, thus providing slices of poor quality. On the other hand, if it were possible for the tissue block to be oriented such that the major blood vessels are perpendicular to the plane of sectioning, slices of much better quality can be obtained. An improved method for preparing tissue is needed to yield usable tissue samples of sufficient quality so as to aid research in the biochemical, pharmacological and toxicological sciences.